The present invention relates to a clearing device that enables some or all of a cake held on the filtering medium of a basket of a centrifugal separator to be broken up.
There are known devices which allow the cake to be removed gradually using the cutting element of a scraper or of a knife. These devices do not allow the entire cake to be extracted because the cutting element must not come into contact with the filtering medium in order not to damage it. That part of the cake which remains in the basket after this stage is known as the residual layer.
More and more often, this residual layer has to be removed because it slows down the filtration which follows or because the user wishes to recover all of the product or not to mix two batches or two different products.
There are already known devices which allow this residual layer to be removed, but these all have their limit or significant shortcomings.
The residual layer may be removed manually using an appropriate tool. This operation absolutely has to involve shutting down and opening the machine. It may therefore prove dangerous to the operator who may come into contact with toxic or inflammable products. What is more, the product may deteriorate when it comes into contact with the open air. Finally, this technique is lengthy and entails the presence of an operator.
Without opening and without shutting down the machine, it is possible to clear away the residual layer by spraying a gas or liquid under pressure. This technique is effective only in about 50% of cases depending on the characteristics of the solid. The spraying of liquid additionally presents the disadvantage of reintroducing liquid onto the product from which liquid has been separated. This option is therefore used only in a few specific instances. The use of mechanical clearing accessories that come into contact with the fabric is only very limited because contact with this scraper damages the filtering medium.
In DE-A-35 18 648 and EP 0 648 542, a flexible and elastically deformable expanding element is inserted between the perforated trough and the filtering medium. When this flexible element is pressurized, the filtering medium is shifted, which causes the cake to be destroyed. This device is suited only to the removal of the residual layer. There are many solvents with which it cannot be used.
Finally, some separators allow the entire cake to be disintegrated and unloaded solely through the movement of the filtering medium. These are, for example, the socalled inversion or fabric-pulling separators. In both instances, the fabric is highly stressed, the size of the machine is fairly limited and the mechanisms are complicated and therefore expensive.